1. Technical Field
The present invention relates to a nitride semiconductor device and a method of manufacturing the same, and, specifically, relates to a field-effect transistor (FET) having normally-off characteristics and the method of manufacturing the same.
2. Background
A high electron mobility transistor (HEMT) using a nitride semiconductor such as gallium nitride (GaN) is expected as a device having high voltage and high speed due to its material properties. It is important to improve the normally-off characteristic, which means stopping the flow of electric current without gate bias applied, in order to achieve the high speed performance of the HEMT.
FIG. 4 is a sectional view illustrating the structure of a HEMT 110 according to the related art disclosed in JP-A-2005-235935. The related art discloses the HEMT 110 including a substrate 101, a semiconductor layer 102 having a buffer layer 121, an electron transit layer 122 and an electron supply layer 123, a source electrode 104, drain electrode 105, and a gate electrode 106 formed within a recess portion 103. In the HEMT 110 described in JP-A-2005-235935, the recess portion 103 is formed by making a portion of the electron supply layer 123 thinner with dry etching.